Plant-herbivore interactions and secondary metabolites of plants: Ecological and evolutionary perspectives

Background: Ancestral and current plant-herbivore associations mediated by secondary compounds have been assessed within the disciplines of paleontology and molecular biology, using the fossil record or DNA sequences. The coevolutionary model of escape and radiation predicts adaptive patterns at both micro-and macro-evolutionary scales, resulting from plant-herbivore interaction. Questions: The study of plant-herbivore interaction and secondary metabolites has been biased for two main reasons: (1) the interdisciplinary study of the interaction that has atomized the field. (2) the conceptual framework of coevolution has favored analyses either within populations or across taxa. Methods: I review the evolutionary history of interaction and secondary metabolites from paleontological and palebiochemical data. Then, based on empirical evidence from quantitative genetics and comparative methods, I examine the main assumptions of the micro-and macro-evolutionary postulates of the coevolutionary model. Further, I overview the analytical approach for the study of plant defense within-species and across phylogenies. Results: Within species, (1) the coevolutionary dynamics shaping plant and herbivore phenotypes, and (2) the role of plant chemistry in constraining ecological interactions, are the most common patterns documented. Across phylogenies, (1) the role of plant chemistry to constrain insect host shifts, and (2) the implications of, and mechanisms behind evolutionary novelties, are more recently assessed. Conclusion: I suggest that future research should integrate both conceptual and analytical perspectives of micro- and macro-evolutionary approaches. One promising direction relies on modern molecular techniques that may open new research avenues by providing evidence for the function of the complex genetic and genomic machineries behind biotic interactions.